Doxies come in two sizes and three coats. Smooth, long-haired and wire-haired. Because of the length of the spine, they are prone to back problems. Maybe not so good a match for an active 9 year old.
My honest opinion, go to your local shelter. There are plenty of young dogs looking for the right family with a child to love them.
If a purebred dog is the only option, then my best advice would be to go to a dog show. Talk to people who have dogs that catch your eye. Since you are looking for a pet for a younger child, maybe some type of terrier. Cairn Terriers are fascinating little creatures, if you ask me. They don't appear to need a lot of grooming and they don't seem to have the boundless energy of you Jack Russell terriers.
Avoid petshops and online kennels. If you can't see the parents with your own two eyes, you don't want the pup. Once you decide on a breed, do some research. Find out about genetic problems that the breed can carry and make sure that the parents of your perspective puppy have been tested and cleared of this problems. Remember that no question is a stupid question and for every question you have for the breeder - they should have 2. A responsible breeder wants to make sure that his/her puppies go to responsible homes. Getting a pup should seem like you are trying to adopt a child. If the breeder just wants your check, then they don't care where their pups go and probably don't care if the pup is healthy.